Hitherto, some investigations have been made about a process for producing a crystalline polymeric sheet which has smooth surfaces and is transparent and high in strength and modulus of elasticity by pultrusion-molding. For example, suggested is a process of pulling out a crystalline polymeric original sheet made of polyethylene, polypropylene, polyacetal resin, nylon or the like into a draw ratio of at least 2.5 or more by means of a pair of rollers heated to a temperature that is not lower than the deformation-start temperature when the temperature of the sheet is raised at a temperature-raising rate of 1° C./minute and that is not over the rise-up temperature of the differential scanning calorimetry melting curve thereof while a load of 10 MPa is applied to the sheet (see, for example, Patent Document 1).    Patent Document 1: JP-A-60-15120
However, in order to draw a polyester resin by the above-mentioned crystalline polymeric sheet producing process, the polyester resin is too hard at low temperature that the resin lacks flexibility necessary for being drawn. At high temperature, orientation-relaxation takes priority. Therefore, in order to yield an oriented sheet excellent in strength and modulus of elasticity, it is necessary to subject the resin to pultrusion-molding in the temperature range from the glass transition temperature of the polyester resin −20° C. to the glass transition temperature +20° C. However, the oriented polyester resin sheet, which is subjected to the pultrusion-molding, has a drawback that when the sheet is heated to the glass transition temperature or higher, modulus of elasticity falls suddenly.
In the meantime, a vinyl chloride based resin is excellent in water resistance, flame resistance, mechanical properties and others, and is further relatively inexpensive; therefore, the resin is widely used as a material for building members. For example, gutters are generally formed by extruding a rigid vinyl chloride based resin.
However, the linear expansion coefficient of rigid vinyl chloride based resin molded bodies is as large as 7.0×10−5 (1/° C.); therefore, when gutters made of rigid vinyl chloride based resin are set up, it is necessary to joint the gutters to each other through a joint which can absorb the stretch and shrinkage of the gutters, or make an end of each of the gutters free. However, when the whole length of the set-up gutters becomes long, the number of joints or shoots becomes large. Thus, there is generated a drawback that the external appearance is bad.
For this reason, various investigations have been made about gutters having a low linear expansion coefficient. For example, suggested is a vinyl chloride based resin gutter comprising a vinyl chloride based resin composition wherein 20 to 35 parts by weight of mica, 20 to 40 parts by weight of calcium carbonate and 5 to 15 parts by weight of a processing aid are added to 100 parts by weight of a vinyl chloride resin (see, for example, Patent Document 2).    Patent Document 2: Japanese Patent No. 2905260
In the gutter, mica and calcium carbonate are added to a vinyl chloride based resin, thereby making the linear expansion coefficient of the gutter low. However, the gutter is made mainly of the vinyl chloride based resin; if the added amount of mica and calcium carbonate is small, the linear expansion coefficient is still high. If the added amount is made high, the gutter has a drawback that the impact resistance and the durability thereof fall.
Suggested is also a gutter which is impregnated with glass fiber as a reinforcing material or a gutter on which a metallic thin plate is laminated. For example, suggested are a composite molded product in which a composite sheet comprising a thermoplastic resin and a reinforcing fiber is shaped to have a required sectional shape, a thermoplastic resin is extruded onto the surfaces thereof to coat the surfaces, and further the reinforcing fiber, which is a short fiber, is oriented at random in at least the shaped region of the composite sheet (see, for example, Patent Document 3), a gutter wherein a metallic thin plate is used as a core member, both surfaces of this core member are each coated with a synthetic resin to form a sheet member, and the tip of a bending tool is pushed against this sheet member to bend/form the member to have a substantially “U-shaped” section, characterized in that a concave groove along which the tip of the bending tool is to be guided is made at an inner-face-side position where the synthetic resin is bent (see, for example, Patent Document 4), and others.    Patent Document 3: JP-A-11-19998    Patent Document 4: JP-A-9-279783
However, in the former gutter, it is essential to form a composite sheet comprising a thermoplastic resin and a reinforcing fiber wherein short fiber pieces are oriented at random, shape the sheet to have a required sectional shape, and subsequently extrude a thermoplastic resin for coating onto the surface thereof; thus, the production is difficult and further when the gutter is disposed of, a problem is caused.
In the latter gutter, a metallic thin plate is laminated as its core member; therefore, the weight becomes large and the work for cutting the gutter is difficult. Furthermore, in ends of the gutter, the metallic thin plate is uncovered; therefore, with the passage of time, the plate rusts so as to result in a drawback that the durability is lowered by corrosion thereof.
Furthermore, as a gutter having a low linear expansion coefficient without using any core member made of a metallic thin plate or any glass fiber, the following is suggested: a polyolefin molded body which has an average linear expansion coefficient of 5×10−5 (1/° C.) or less at temperatures of 20 to 80° C. and is obtained by putting, onto a surface of a polyolefin oriented material having an average linear expansion coefficient of 5×10−5 (1/° C.) or less at temperatures of 20 to 80° C., a low molecular weight compound in which the polyolefin can be dissolved, and then pressing/heating the resultant to bond the polyolefin oriented material (see, for example, Patent Document 5). Suggested are also a synthetic resin gutter in which a thermoplastic synthetic resin has a linear expansion coefficient of 6×10−5/° C. or less and a thickness of more than 0.5 mm and is obtained by extruding a thermoplastic resin, and then drawing this extruded body to stretch the body, thereby orienting molecules therein in a single direction (see, for example, Patent Document 6), and others.    Patent Document 5: JP-A-10-291250    Patent Document 6: JP-A-2002-285685
However, the former gutter is a sheet wherein a polyolefin oriented material is highly drawn into a draw ratio of 20 to 40, and thus the gutter has drawbacks that the gutter is easily cracked along the draw direction and the impact resistance is poor. When an attempt is made to laminate a rigid vinyl chloride based resin, AES resin or the like thereon in order to prevent the drawbacks, there is generated a drawback that the oriented state of the polyolefin is turned into disorder to make the linear expansion coefficient high since the polyolefin has a lower melting point than the above-mentioned resins.
Additionally, the latter gutter has drawbacks that the gutter is easily cracked along the draw direction and the impact resistance is poor since the gutter is produced only by drawing a gutter obtained by extrusion molding.